1. Field of the Invention
This invention relates generally to semiconductor fabrication, and more particularly to a method of removing contaminants from a semiconductor vacuum processing chamber.
2. Description of the Related Art
Many semiconductor fabrication processes occur in reduced pressure and/or gas flow environments. Examples of such processes are legion, and include techniques such as physical vapor deposition (sputter) (xe2x80x9cPVDxe2x80x9d), chemical vapor deposition (xe2x80x9cCVDxe2x80x9d) and low pressure dry etching, to name just few. These various low pressure processes are carried out in a processing chamber in one form or another that incorporates one or possibly several types of vacuum systems. In some fabrication process, such as low pressure dry etching, the requirement for high and ultra vacuum regimes is dictated by the necessity for low operating pressures. In others, such as PVD and various CVD processes, the requirement for high vacuum is dictated by the need to remove gaseous contaminants from the processing chamber prior to the introduction of wafers for processing. The presence of contaminants, such as water, nitrogen and carbon dioxide in the chamber can radically degrade the performance of thin films deposited by PVD and CVD processes.
Metallization layers are particularly sensitive to contamination by residual gaseous particles in a processing chamber. Such gaseous contaminants frequently are the result of outgassing from the chamber walls of molecules left over from previous processing. In other circumstances, gaseous contaminants flow into the processing chamber during maintenance of the chamber, when the chamber is opened to the atmosphere for maintenance. Irrespective of their particular origin, contaminants in the vacuum chamber can significantly impact the resistivity, grain structure, surface texture, reflectivity, step coverage, electromigration and circuit reliability associated with a deposited metal film.
Three high vacuum pump systems that have historically been used with vacuum processing chambers include diffusion pumps, turbomolecular pumps and cryopumps. Diffusion pumps utilize a supersonic flow of atomized oil droplets to induce movement of gas particles from the chamber. Turbomolecular pumps operate much like well known turbine pumps that utilize a rotating shaft and a plurality of cooperating rotor and stator blades. Cryopumps are closed cycle refrigerator pumps that remove gases from the vacuum chamber by capturing them on a cold surface, either through the process of cryocondensation or cryosorption. Although these three pumping systems can achieve vacuums greater than 10xe2x88x927 torr, they nevertheless exhibit certain limitations. Diffusion pumps produce some degree of oil backstreaming that can lead to oil contamination of the vacuum chamber, while all three pumping systems have pumping speed limitations. The limits on pumping speed are largely the result of the requirement for the throttling the flow into the pump from the chamber through the use of one or more throttling valves.
Conventional ultra and high vacuum processing chambers, such as those commonly used for PVD and CVD processes, require extensive physical pump down times and test wafer conditioning to remove gaseous contaminants from the processing chamber so that the production of high quality films is ensured. In those processing chambers that incorporate plasma processes, the chamber conditioning involves both a lengthy pump down and one or more test wafer conditioning steps. The pump down is typically carried out using one of the aforementioned high vacuum pumping systems alone or in combination with the others. The test wafer conditioning process involves the placement of a conditioning test wafer, which is either a bare silicon wafer or a silicon wafer coated with a silicon dioxide film, in the vacuum chamber and the subsequent creation of a plasma ambient which dissociates gaseous contaminant molecules into lighter species which may be pumped away from the vacuum chamber. An inert gas, such as argon, is frequently the ambient of choice for the plasma test wafer conditioning process. Depending upon the volume of the vacuum chamber, the overall chamber conditioning, including the chamber pump down and plasma test wafer conditioning process, may last from a few hours to one or more days.
While the incorporation of plasma based test wafer conditioning speeds the conditioning of a vacuum chamber and improves the overall vacuum quality thereof, many semiconductor processing chambers do not utilize plasma processes and reactions, and thus cannot take advantage of the benefits of test wafer conditioning through plasma processing. Examples of these non-plasma based processing chambers are legion, and include load locks, orientors, degassing, cool down chambers, passthrough chambers, buffers, rapid thermal processing chambers and holding chambers to name just a few. In such non-plasma processing, the conditioning of the vacuum chamber is carried out through pumping means only.
The main disadvantages associated with the conventional methods of conditioning vacuum chambers is the cost associated with the consumption of conventional conditioning wafers and the sheer length of the conditioning process due to the relatively slow pumping speeds of high vacuum pump systems. This speed phenomena is particularly germane to the multitudes of non-plasma based processing chambers, which cannot take advantage of the speed enhancing characteristics of plasma based test wafer conditioning.
In some previously used vacuum processing tools, a titanium gettering pump is coupled to the vacuum chamber to improve the vacuum characteristics in the chamber. A typical titanium gettering pump includes a sputter chamber connected and open to the processing chamber that is designed to sputtered titanium into vapor phase. Interatomic attractive forces between the titanium vapor and hydrogen, oxygen and water vapor draw the hydrogen, oxygen and water out of the processing chamber and into the gettering pump.
Titanium gettering pumps present certain disadvantages. The technique inherently involves some contamination of the processing chamber with titanium and the species used to sputter the titanium into vapor phase. This leads to difficult maintenance issues. In addition, titanium gettering pumps have limited ability to provide very low pressures.
The present invention is directed to overcoming or reducing the effects of one or more of the foregoing disadvantages.
In accordance with one aspect of the present invention, a method of removing gaseous phase contaminants from a processing chamber is provided that includes placing a heated titanium film in the processing chamber to dissociate a first portion of the gaseous phase contaminants and capture a second portion of the gaseous phase contaminants. The dissociated gaseous phase contaminants are pumped from the processing chamber and the titanium film is removed from the processing chamber.
In accordance with another aspect of the present invention, a method of removing gaseous phase water from a processing chamber is provided that includes placing a heated substrate that has a titanium film in the processing chamber to dissociate a first portion of the gaseous phase water into hydrogen and oxygen and capture some of the oxygen in the titanium film. The dissociated hydrogen and uncaptured oxygen are pumped from the processing chamber and the substrate is removed from the processing chamber.
In accordance with another aspect of the present invention, a method of removing gaseous phase contaminants from a processing chamber is provided that includes placing a first substrate in the processing and introducing a plasma ambient to remove some of the gaseous phase contaminants. A heated substrate that has a titanium film is placed in the processing chamber to dissociate a first portion of the gaseous phase contaminants and capture a second portion of the gaseous phase contaminants. The dissociated gaseous phase contaminants are pumped from the processing chamber and the substrate is removed from the processing chamber.